Method for forming thermal spray coating film of intermetallic compound, thermal spray coating film, method for producing metal product having spray coating film and glass-conveying roll

ABSTRACT

To provide a method for forming a thermal spray coating film, by forming a thermal spray coating film of an Al—Fe based intermetallic compound having a high hardness, on a metal substrate. 
     A method for forming a thermal spray coating film, by forming a thermal spray coating film of an Al—Fe based intermetallic compound, from a mixture of an Al—Fe based intermetallic compound powder composed mainly of FeAl 2  and a metal powder composed mainly of Fe, as feedstock, on the surface of a metal substrate.

TECHNICAL FIELD

The present invention relates to a method for forming a thermal spraycoating film of an intermetallic compound on the surface of a metalsubstrate, and a thermal spray coating film of an intermetalliccompound. In particular, the present invention relates to a method forforming a thermal spray coating film of an Al—Fe based intermetalliccompound, on the surface of a metal substrate made of iron or aniron-based alloy, and a thermal spray coating film of an intermetalliccompound formed. Further, the present invention relates to a method forproducing a metal product comprising a metal substrate having thethermal spray coating film, by the method of forming the thermal spraycoating film, and a glass-conveying roll comprising a metal producthaving the thermal spray coating film.

BACKGROUND ART

Heretofore, in a step for producing a glass plate by float process, avariety of glass-conveying rolls such as a lift-out roll for pulling upa continuous layer of high-temperature glass, called a glass ribbon,flowing on the upper surface of molten tin, from a tin bath, and a lehrroller for moving the glass ribbon in a furnace that gradually cools theglass ribbon while moving it, are used.

The glass-conveying rolls, which are contacted directly with a hightemperature glass before cooling for solidification, affect the qualityof a glass plate. For example, a glass ribbon immediately after beingtaken out from a tin bath has a sufficiently high temperature, and ifthe surface of a roll is made of a metal composed mainly of iron,microscopic adhesion easily occurs between the roll and the glassribbon. Further, upon moving of the glass ribbon on the roll, the glassadhering thereto tends to be peeled from the ribbon and remain on thesurface of the roll. Since a metal roll is excellent in heat conduction,a minute glass residue adhering to the surface of the metal roll iseasily deprived of heat and solidified, and thereby scratches thesurface of a glass ribbon subsequently conveyed.

Further, on the lower surface of the glass ribbon pulled up from the tinbath, a small amount of metal tin or tin oxide is deposited. At the timeof conveying such a glass ribbon by a metal roll, a part of the deposittends to be firmly adhered to the surface of the conveying roll, andthereby scratch the surface of a glass ribbon, like the above-mentionedglass residue.

Furthermore, in a process of conveying a glass ribbon or a glass plate,there is a case where sulfur oxide gas is made to flow for applying aprotective film made of a sulfuric acid compound on the lower surface ofthe glass. In such a case, the surface of the metal roll tends tocorrode, and, as a result, contaminate the glass, but no corrosionoccurs in the case of a ceramic coating.

Therefore, a glass-conveying roll having a ceramic thermal spray coatingfilm applied on the surface of a roll base material made of a metal, andhaving a metal layer or a cermet thermal spray coating film interposed,as a bond layer, between the roll base material and the ceramic thermalspray coating film, has been proposed.

For example, Patent Document 1 discloses a convey roll having a ceramicthermal spray coating film formed on the surface of a roll basematerial, and further having a bond coat made of cermet interposedbetween the base material and the ceramic thermal spray coating film.

Further, Patent Document 2 discloses a float glass-producing roll havinga ceramic thermal spray coating film applied on the surface of a metalsubstrate of a roll body portion, and further having a metal thermalspray coating film with a linear thermal expansion coefficient which isthe medium between that of the metal substrate and that of the ceramicthermal spray coating film, interposed between the metal substrate andthe ceramic thermal spray coating film.

In Patent Documents 1 and 2, a ceramic thermal spray coating film isformed so as to suppress deposit of a glass residue or a tin aggregate,and at the same time a bond coat containing a metal between a roll basematerial and a ceramic thermal spray coating film is formed to suppressdelamination of the ceramic thermal spray coating film due to thedifference in linear thermal expansion coefficient between that of theceramic thermal spray coating film and that of the roll base material.

On the other hand, if a metal coating film having the same function asthe ceramic thermal spray coating film and further having substantiallythe same linear thermal expansion coefficient as the roll base material,is formed on the surface of the roll base material, it is possible tosuppress delamination of the ceramic thermal spray coating film due todifference in linear thermal expansion coefficient with the roll basematerial.

For the purpose of improving oxidation resistance, corrosion resistance,wear resistance and non-adhesive to a metal of the metal substrate,attempts have been made to form a diffusion coating film on the surfaceof a metal substrate by calorizing treatment (Patent Documents 3 to 5).

Al diffused to the surface of a metal substrate forms an intermetalliccompound with a metal material on the surface of the substrate. In acase where the metal substrate is made of iron or an iron-based alloysuch as stainless steel, an Al—Fe based intermetallic compound isformed.

However, calorizing treatment has the following problems.

(1) Size of a treatment furnace is restricted since the treatment isbatch treatment.

(2) A metal substrate may deteriorate due to high-temperature treatmentin the vicinity of 1,000° C.

(3) As shown in the after-mentioned Examples, a coating film formed bycalorizing treatment is brittle, and therefore the coating film may bepeeled from the metal substrate when used for a glass-conveying roll.

On the other hand, it has been studied to form an Al—Fe based thermalspray coating film on the surface of a metal substrate (Non-PatentDocuments 1 to 3).

However, a conventional Al—Fe based thermal spray coating film has thefollowing problems.

In the case of forming an Al—Fe based thermal spray coating film, anFe—Al based alloy powder having an Al content of 25 weight % is widelyused as feedstock for thermal spray coating, therefore a mainconstituent phase of a thermal spray coating film formed is FeAl, andsuch a compound has high ductility as an intermetallic compound. In anapplication where ductility is required for the thermal spray coatingfilm, the ductility is preferred film properties, but in a case wheresuch a film is applied to a glass-conveying roll, there are problemsfrom the viewpoint of low hardness, and a possibility of hydrogenbrittleness due to formation of excess pores by quenching.

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: JP-A-2004-277828-   Patent Document 2: JP-A-H4-260623-   Patent Document 3: JP-A-H10-219426-   Patent Document 4: JP-A-2009-263692-   Patent Document 5: JP-A-2015-229787

Non-Patent Documents

-   Non-Patent Document 1: J. M. Guilemany, C. R. C. Lima, N.    Cinca, J. R. Miguel, ‘Studies of Fe-40Al coatings obtained by high    velocity oxy-fuel’, Surface & Coatings Technology 201 (2006)    2072-2079.-   Non-Patent Document 2: Hong-Tao Wang, Chang-Jiu Li, Guan-Jun Yang,    Cheng-Xing Li, ‘Cold spraying of Fe/AI powder mixture: Coating    characteristics and influence of heat treatment on the phase    structure’, Applied Surface Science 255 (2008) 2538-2544.-   Non-Patent Document 3: J. M. Guilemany, N. Cinca, J. Fernandez,    and S. Sampath, ‘Erosion, Abrasive, and Friction Wear Behavior of    Iron Aluminide Coatings Sprayed by HVOF’, Volume 17(5-6)    Mid-December 2008 Journal of Thermal Spray Technology.

DISCLOSURE OF INVENTION Technical Problem

In order to solve the above-described problems of prior art, it is anobject of the present invention to provide a method for forming athermal spray coating film of an Al—Fe based intermetallic compoundhaving high hardness, on a metal substrate, and a coating film of anintermetallic compound.

Solution to Problem

In order to achieve the above object, the present invention provides amethod for forming a thermal spray coating film, by forming a thermalspray coating film of an Al—Fe based intermetallic compound, on thesurface of a metal substrate, from a mixture of an Al—Fe basedintermetallic compound powder composed mainly of FeAl₂ and a metalpowder composed mainly of Fe, as feedstock.

In the method of the present invention, it is preferred that a blendratio of the intermetallic compound powder to the metal powder is from70/30 to 80/20 by the weight ratio.

Further, in the method of the present invention, it is preferred that aweight ratio (Al/Fe) of Al to Fe in the mixture is from 0.55 to 0.85.

Further, in the method of the present invention, it is preferred that aweight ratio (Al/Fe) of Al to Fe in the intermetallic compound powder isfrom 0.90 to 1.15.

Further, in the method of the present invention, it is preferred that aproportion of FeAl₂ in the intermetallic compound powder is at least 75weight %.

Further, in the method of the present invention, it is preferred that aproportion of Fe in the metal powder is at least 70 weight %.

Further, in the method of the present invention, it is preferred that aconstituent material of the surface of the metal substrate is iron or aniron-based alloy.

Further, in the method of the present invention, it is preferred thatthe thermal spray coating film has a film-thickness of from 0.05 to 1.5mm.

Further, the present invention provides a method for producing a metalproduct, comprising:

forming a thermal spray coating film of an Al—Fe based intermetalliccompound on the surface of a metal substrate by the above method forforming a thermal spray coating film, to produce a metal productcomprising the metal substrate having the thermal spray coating film.

It is preferred that a metal product produced in the production methodof the present invention is a glass-conveying roll.

In order to achieve the above object, the present invention provides athermal spray coating film of an Al—Fe based intermetallic compound,which has a multi-phase structure in a scanning electron microscopic(SEM) image showing a cross section of the thermal spray coating film ofan Al—Fe based intermetallic compound.

Further, in the present invention, it is preferred that a weight ratio(Al/Fe) of Al to Fe in the thermal spray coating film is from 0.55 to0.85.

Further, in the present invention, it is preferred that the thermalspray coating film contains Al₂O₃ particles having a size of less than 5μm.

Further, in the present invention, it is preferred that a distancebetween Al₂O₃ particles being present within 50 μm from the surfacelayer of the thermal spray coating film, is at least 5 μm.

Further, the present invention provides a glass-conveying rollcomprising a metal roll having the thermal spray coating film on thesurface.

Advantageous Effects of Invention

The thermal spray coating film of an Al—Fe based intermetallic compoundformed by the method of the present invention has a high hardness ascompared with a conventional Al—Fe based thermal spray coating film, andhas no concern about hydrogen embrittlement by quenching.

Further, the thermal spray coating film of an Al—Fe based intermetalliccompound formed by the method of the present invention has a hightoughness as compared with a coating film of an Al—Fe basedintermetallic compound formed by calorizing treatment, and a metalsubstrate will not reach high temperature during the treatment. Further,in the case of the above thermal spray coating film formed by thepresent invention, various size and shape of a substrate is applicableas compared with a calorizing method in which a closed container isneeded.

Further, a difference in linear thermal expansion coefficient with ametal substrate the surface of which is made of iron or an iron-basedalloy is small, and therefore it is possible to suppress peeling of thecoating film due to the difference in linear thermal expansioncoefficient.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an Al—Fe based equilibrium diagram.

FIG. 2(a) is an SEM image showing a cross section of the thermal spraycoating film in Ex. 1.

FIG. 2(b) is a magnified image in the vicinity of a surface side of thethermal spray coating film in FIG. 2(a).

FIG. 2(c) is a mapping image of Al analyzed by EDS of the imaging partof FIG. 2(b).

FIG. 2(d) is a mapping image of 0 analyzed by EDS of the imaging part ofFIG. 2(b).

FIG. 3(a) is an SEM image showing a cross section of a coating filmformed by calorizing treatment.

FIG. 3(b) is a magnified image in the vicinity of a surface side of athermal spray coating film in FIG. 3(a).

FIG. 3(c) is a mapping image of Al analyzed by EDS of the imaging partof FIG. 3(b).

FIG. 3(d) is a mapping image of 0 analyzed by EDS of the imaging part ofFIG. 3(b).

FIG. 4(a) is a graph showing an EDS analysis result of a coating filmformed by calorizing treatment, and FIG. 4(b) is an SEM image at ameasurement part thereof.

FIG. 5 is a metallographic microscope image of indentations by a Vickershardness tester diamond indenter pressed into the cross section of eachof the coating film of Ex. 1 and the coating film of Comp. Ex. 1.

FIG. 6 is an image of an Sn wettability evaluation sample in each of Ex.2 and Comp. Ex. 3.

FIG. 7 is an image of an Sn wettability evaluation sample after heatingin each of Ex. 2 and Comp. Ex. 3.

FIG. 8 is an image of an Sn wettability evaluation sample after heatingin each of Ex. 2 and Comp. Ex. 3.

FIG. 9 is an image of a glass wettability evaluation sample in each ofEx. 3 and Comp. Ex. 4.

FIG. 10 is an image of a glass wettability evaluation sample afterheating in each of Ex. 3 and Comp. Ex. 4.

DESCRIPTION OF EMBODIMENTS

Now, the present invention will be explained below. The method of thepresent invention relates to a method for forming a thermal spraycoating film of an Al—Fe based intermetallic compound on the surface ofa metal substrate.

The metal substrate of the present invention is a metal substrate usedin an application where heat resistance, molten metal resistance,corrosion resistance at high temperature, wear resistance andnon-adhesive to a metal or a glass are required, such as aglass-conveying roll. Further, a metal component (such as a componentfor sealing or a brick receiving component) having a portion exposed toan atmosphere of a float bath in a float glass production equipment, asdescribed in WO2010/070982, may be mentioned.

In the metal substrate in the present invention, a constituent materialof the surface on which a thermal spray coating film of an Al—Fe basedintermetallic compound is formed is mainly iron or an iron-based alloysuch as stainless steel.

The metal substrate in the present invention is such that theconstituent material of the entire metal substrate may be iron or aniron-based alloy, or that only a constituent material of the surface onwhich the thermal spray coating film of an Al—Fe based intermetalliccompound is formed may be iron or an iron-based alloy. In the lattercase, a constituent material other than that of the surface on which thethermal spray coating film of an Al—Fe based intermetallic compound isformed, may be a light-weight metal material such as aluminum, analuminum alloy, magnesium or a magnesium alloy, or a ceramic materialmay be used.

In the method of the present invention, as the feedstock for thermalspray coating, a mixture of an Al—Fe based intermetallic compound powdercomposed mainly of FeAl₂ and a metal powder composed mainly of Fe, isused.

FIG. 1 is an Al—Fe based equilibrium diagram referred from database ofthermodynamic equilibrium calculation software FactSage (Ver. 6.3,manufactured by Research Center of Computational Mechanics, Inc.). Asshown in FIG. 1, in the Al—Fe based intermetallic compound, multipleconstituent phases are present depending on proportions of Al and Fe anda temperature range of an eutectic reaction. FeAl₂ is produced inproportions of Al being from 60 to 70 at % and Fe being from 30 to 40 at% and a temperature range of an eutectic reaction being from 1,000 to1,200° C.

Due to brittleness as compared with FeAl as a main constituent phase ofa conventional Al—Fe based thermal spray coating film, a bulk product ofthe Al—Fe based intermetallic compound is crushed by combining knownmeans such as coarse grinding method by e.g. a cutter mill or a jawcrusher, and a fine grinding method by e.g. a ball mill or a planetarymill, to obtain an Al—Fe based metal compound powder.

Here, the bulk material of the Al—Fe based intermetallic compound may,for example, be obtained by melting an Fe feedstock and an Al feedstockby a known means such as electric heating or arc melting in anon-oxidative atmosphere or vacuum, followed by cooling.

In this specification, in the case of describing an Al—Fe basedintermetallic compound powder composed mainly of FeAl₂, it is preferredthat the proportion of FeAl₂ in the Al—Fe based intermetallic compoundpowder is at least 75 weight %. The reason to use the Al—Fe basedintermetallic compound powder having a proportion of FeAl₂ of the aboveranges, is as follows.

FeAl having less Al amount than FeAl₂ has a high ductility as anintermetallic compound, and it is therefore difficult to efficientlygrind it by the above-mentioned method. On the other hand, Fe₂Al₅ orFeAl₃ having more Al amount than FeAl₂ is exceedingly oxidized bygrinding.

In this specification, the Al—Fe based intermetallic compound powderdescribed hereinafter indicates the above-defined Al—Fe basedintermetallic compound powder composed mainly of FeAl₂.

The proportion of FeAl₂ in the Al—Fe based intermetallic compound powderis more preferably at least 80 weight %, furthermore preferably at least85 weight %.

The Al—Fe based intermetallic compound powder may contain a constituentphase other than FeAl₂, as long as the proportion of FeAl₂ satisfies theabove range. As the constituent phase other than FeAl₂, FeAl or Fe₂Al₅may, for example, be mentioned. It is preferred that the weight ratio(Al/Fe) of Al to Fe in the Al—Fe based intermetallic compound powder isfrom 0.90 to 1.15. FeAl₂ is such that the weight ratio of Al to Fe is1.0 (50Al-50Fe). When the weight ratio (Al/Fe) of Al to Fe in the Al—Febased intermetallic compound powder is from 0.90 (47 Al-53Fe) to 1.15(53Al-47Fe), it is possible to satisfy the above-mentioned proportion ofFeAl₂ in the Al—Fe based intermetallic compound powder.

Further, the weight ratio (Al/Fe) of Al to Fe in the Al—Fe basedintermetallic compound powder is almost same as the weight ratio (Al/Fe)of Al to Fe in a feedstock used in preparation of a bulk material of theAl—Fe based intermetallic compound by the above-mentioned procedure.Accordingly, when the weight ratio of Al to Fe in a feedstock used inpreparation of the bulk material of the Al—Fe based intermetalliccompound is from 0.90 to 1.15, the weight ratio (Al/Fe) of Al to Fe inthe Al—Fe based intermetallic compound powder obtainable by grinding thebulk material of the Al—Fe based intermetallic compound is from 0.90 to1.15, whereby it is possible to obtain the Al—Fe based intermetalliccompound powder composed mainly of FeAl₂.

The weight ratio (Al/Fe) of Al to Fe in the Al—Fe based intermetalliccompound powder is more preferably from 0.95 (49Al-51 Fe) to 1.10(52Al-48Fe).

As the metal powder composed mainly of Fe, a powder of Fe or a powder ofa Fe-based alloy such as a binary alloy such as a Fe—Al alloy or a Fe—Cralloy or stainless steel, may be used. In this specification, in thecase of describing the metal powder composed mainly of Fe, theproportion of Fe in the metal powder is preferably at least 70 weight %.The reason to use a metal powder having a proportion of Fe within theabove range, is as follows.

If the proportion of Fe is less than 70 weight %, such an element ismore likely to form a compound with Fe and Al in a production process ofa coating film or an application environment at a high temperature,whereby a coating film is likely to be, for example, more brittle, andtherefore advantageous properties of the coating film may deteriorate.

In this specification, the above-defined metal powder composed mainly ofFe is hereinafter referred to as a Fe based metal powder.

The Fe based metal powder may be obtained by a known method such as anatomization method, a reduction method or an electrolytic method.

In the method of the present invention, in the above mixture, a blendratio of the Al—Fe based intermetallic compound powder to the Fe basedmetal powder is preferably from 70/30 to 80/20 by a weight ratio, forthe following reasons.

If the amount of the Al—Fe based intermetallic compound powder is toolarge, oxidation during preparation of a mixed powder easily proceeds,and as a result, it becomes difficult to obtain a dense thermal spraycoating film. On the other hand, if the amount of the Fe powderincreases, a reaction to form a new intermetallic compound from Fe andAl, as an exothermic reaction, is activated during the thermal spraycoating, and therefore it is impossible to obtain a coating film havingstable properties.

The blend ratio of the Al—Fe based intermetallic compound powder to theFe based metal powder is more preferably from 73/27 to 77/23.

In the above mixture, the weight ratio (Al/Fe) of Al to Fe is preferablyfrom 0.55 to 0.85. In a case where the weight ratio (Al/Fe) of Al to Feis from 0.55 to 0.85, the constituent phase of the intermetalliccompound is FeAl+FeAl₂ as shown in FIG. 1.

Therefore, in a case where the above mixture is used as a feedstock forthermal spray coating, a thermal spray coating film formed becomes acoating film having a multi-phase structure containing FeAl, FeAl₂ andFeAl—FeAl₂ as a constituent phase.

The coating film having a multi-phase structure containing FeAl, FeAl₂and FeAl—FeAl₂ (hereinafter referred to as a coating film having amulti-phase structure of an Al—Fe based intermetallic compound), showsthe following effects.

As shown in the after-mentioned Examples, a coating film formed bycalorizing treatment is brittle, and therefore the coating film crackedonly by polishing the surface of the coating film after cutting a samplefor photographing a scanning electron microscopic (SEM) image showing across section of the coating film, by a wire electrical dischargemachine.

On the other hand, the coating film having a multi-phase structure of anAl—Fe based intermetallic compound has a sufficient toughness.

Such a difference can be estimated by comparing a constituent phaseexpected from results of an SEM image showing a cross section of acoating film formed by calorizing treatment, an energy dispersible X-rayspectrometry (EDS), and a mapping image in the vicinity of a surfaceside of the cross section of the coating film by EDS' and a structure ofthe present invention.

In the case of the coating film formed by the calorizing treatment, adiffusion layer is present between the metal substrate and the Al—Febased intermetallic compound, the coating film itself appears to bealmost uniform as a whole, the weight ratio of Fe to Al is close to 1,and therefore it can be estimated that most of the constituent phase isbrittle FeAl₂. However, a part of the surface layer of the cross sectionof the coating film has a region where from 5 to 10 μm of Al₂O₃ isagglomerated.

On the other hand, in the case of the coating film having a multi-phasestructure of an Al—Fe based intermetallic compound, FeAl havingductility, formed by the reaction with a metal feedstock during thethermal spray coating, is present in the vicinity of FeAl₂ even whenmost of the constituent phase of the Fe—Al intermetallic compound isFeAl₂, and as a result, a coating film produced has a strong toughnessas compared with the calorized coating film. Further, as is differentfrom the calorizing treatment, fine Al₂O₃ is dispersed in the coatingfilm. Al₂O₃ dispersed in the coating film is preferably less than 5 μm,more preferably at most 3 μm. Further, a distance between the Al₂O₃having a size of less than 5 μm, being present within 50 μm from thesurface layer of the cross section of the coating film, is preferably atleast 5 μm, more preferably at least 10 μm.

With respect to the thermal spray coating film of an Al—Fe basedintermetallic compound of the present invention, a mixed powder of theAl—Fe based intermetallic compound powder and the Fe based metal powderis flattened and laminated, by heat and collision energy in the thermalspraying process, to form a multi-phase structure. By Al contained inthe powder being oxidized when the heated mixed powder is deposited,Al₂O₃ is present at interfaces where flattened particles are piled up.When the mixed powder of the Fe based metal powder is flattened andlaminated, particles laminated are less likely to fall off from thecoating film. On the other hand, according to a method such ascalorizing treatment, Al₂O₃ exhibits a high-temperature corrosionresistance to SO₂ but agglomerates at a part of the surface layer toform agglomerates and thereby becomes inhomogeneous, and due to thedifference in thermal expansion coefficient at the time of heating, athermal stress is generated at the portion thereby to form fractures orcracks in the coating film, and therefore the coating film tends to peelor partly fall off when used as a glass-conveying roll. Further, it hasbeen known that the calorized layer loses its effect as a modified layerbecause Al is easily diffused in the substrate when it becomes about900° C. On the other hand, in the case of the thermal spray coating filmof the Al—Fe based intermetallic compound of the present invention, itis possible to reduce the deterioration of the effect as the modifiedlayer, as mentioned in e.g. calorizing treatment, because it has manyinterfaces in the modified layer and has no diffusion layer.

A conventional Al—Fe based thermal spray coating film containing FeAl asa main constituent phase, as shown in the after-mentioned Examples, haslow hardness, and therefore it is not suitable for applications wherethe coating film is considered to be in contact with other components.Further, a single phase material such as alumina having a B2 structure,such as FeAl, may form a plurality of pores usually by quenching, andtherefore undesirable properties such as hydrogen brittleness areconsidered to become apparent.

It is considered that this is due to ductility of FeAl in the mainconstituent phase of the thermal spray coating film.

On the other hand, the thermal spray coating film of the Al—Fe basedintermetallic compound of the present invention, which is a coating filmhaving a multi-phase structure containing FeAl, FeAl₂, and FeAl—FeAl₂,has high surface hardness and further will not have a plurality of poresformed even by quenching.

Further, when the weight ratio (Al/Fe) of Al to Fe in the mixture isfrom 0.55 to 0.85 as shown in the after-mentioned Examples, the averagethermal expansion coefficient of the thermal spray coating film of theintermetallic compound in a temperature range of from room temperatureto 700° C., is substantially the same as that of stainless steel(SUS304) widely used as a metal substrate of a glass-conveying roll, andtherefore peeling of the coating film when used as a glass-conveyingroll is reduced.

Further, the Vickers hardness of soda lime silicate glass is about 530at room temperature, but is estimated to be lower than the Vickershardness of the thermal spray coating film of the Al—Fe basedintermetallic compound in a temperature range of from 400 to 800° C.Accordingly, the coating film may not be damaged by e.g. a cullet whenused as a glass-conveying roll.

In the method of the present invention, the weight ratio (Al/Fe) of Alto Fe in the mixture is more preferably from 0.60 to 0.80.

The feedstock for thermal spray coating used in the method of thepresent invention can be prepared as follows.

The Al—Fe intermetallic compound powder and the Fe based metal powderare respectively weighed, and mixed and crushed in an organic solventsuch as ethanol, using a rotary ball mill or a vibratory ball mill.Needless to say, in order to obtain an excellent properties powder, itis usually advantageous that these feedstock powders have a higherpurity and are fine. In particular, in order to ensure homogeneity ofthe thermal spray coating powder, it is preferred that the Al—Fe basedintermetallic compound powder and the Fe based metal powder have anaverage particle size of at most 10 μm.

The powder ground and mixed by e.g. a rotary ball mill (or a vibratoryball mill) is fine and thus is not suitable as a thermal spray coatingpowder when used as it is, and therefore it is preferred to carry outgranulation process using e.g. a spray dryer in a non-oxidativeatmosphere and adding an organic binder. The organic binder to be usedis preferably one which is easily removed during sintering, such as anacrylic resin or polyethylene glycol. The granurated powder is usuallyspherical and has good flowability, but is not hard enough to withstandconveyance by pressurized gas.

When this granulated powder is calcined at a temperature of from 800 to1,000° C. in a non-oxidative atmosphere such as vacuum or Ar, theorganic binder is removed, and at the same time primary particles in thegranulated powder are sintered with one another while keeping sphericalshape. When the resulting powder is crushed, it becomes roughlyspherical, and is less likely to easily collapse even when conveyed bypressurized gas.

Such spherical porous particles thus obtained are classified so as tohave specified particle sizes, and then used as feedstock for thermalspray coating. A preferred average particle size is from 10 to 100 μm,more preferably from 15 to 75 μm.

Here, the above average particle size is calculated as follows. Usingsieves prescribed in JIS Z8801, several sieves having different sieveopenings are piled up in ascending order from the smallest opening, andvibration is imparted at a constant time with a constant amplitude. Themass of the sample remaining on each sieve was measured, a cumulativedistribution of the mass was described in a graph, and the particle sizecorresponding to the cumulative value of the particle size distributionbeing 50% was treated as the average particle size.

The thermal spray coating method used in the method of the presentinvention is not particularly limited, but is preferably a high velocityoxygen fuel method or an atmospheric plasma spraying method.

The thickness of the coating film formed in the method of the presentinvention is not particularly limited, but is preferably from 0.05 to1.5 mm, more preferably from 0.1 to 1.0 mm.

The coating film formed by the method of the present invention has thefollowing preferred properties in addition to the above mentioned point.

The coating film formed by the method of the present invention, which iscomposed of an Al—Fe intermetallic compound, is excellent innon-adhesive to molten tin and glass. Further, the coating film isexcellent in high-temperature corrosion resistance to SO₂ which can bepresent in an atmosphere where a glass-conveying roll is controlled.

Proposed is a method wherein a coating film of metal aluminum is formedby a hot dip plating method on the surface of an iron based metalcomponent, and utilizing a reaction of a substrate with a coating layerby heat treatment of the component, so as to change the coating film ofmetal aluminum to a state where multiple Fe—Al based intermetalliccompounds such as FeAl and FeAl₂ are present. However, such a method issignificantly different from the technique of the present invention fromthe viewpoint that it is difficult to control a structure and ratio ofpresence of the precipitation phase of the coating layer and that heattreatment after coating is essential.

Further, the present invention relates to a method for producing a metalproduct by forming a thermal spray coating film of an Al—Fe basedintermetallic compound on the surface of a metal substrate by the methodfor forming a thermal spray coating film of the present invention, toproduce a metal product comprising the metal substrate having thethermal spray coating film.

The metal product of the present invention is a metal product used forapplications requiring heat resistance, molten metal resistance, hightemperature corrosion resistance, wear resistance, non-adhesive to ametal or a glass, and rigidity of a structure at a high temperature.Particularly preferred is a metal product having a surface to be incontact with a molten glass or a glass formed product at a hightemperature (such as a glass ribbon drawn out from a float bath). Inparticular, for example, a metal component (such as a component forsealing or a brick receiving component) having a portion exposed to anatmosphere of a float bath in a float glass production equipment, or aglass-conveying roll, may be mentioned.

Particularly preferred is a glass-conveying roll to be in contact with aglass ribbon drawn out from a float bath.

Further, the present invention is a thermal spray coating film of anAl—Fe based intermetallic compound, which has a multi-phase structure ina scanning electron microscopic (SEM) image showing a cross-section ofthe thermal spray coating film of an Al—Fe based intermetallic compound.

The composition of the thermal spray coating film is substantially thesame as the composition of the mixture used in its formation. That is,the thermal spray coating film of the present invention preferably has aweight ratio (Al/Fe) of Al to Fe being from 0.55 to 0.85. Further, Al₂O₃particles in the thermal spray coating film preferably have a size ofless than 5 μm as mentioned above, and further as mentioned above, it ispreferred that a distance between the Al₂O₃ particles being presentwithin 50 μm from the surface layer of the thermal spray coating film isat least 5 μm.

Furthermore, the present invention provides a glass-conveying rollcomprising a metal roll having the thermal spray coating film on itssurface.

EXAMPLES

Now, the present invention will be described in further detail withreference to Examples, but the present invention is by no meansrestricted thereto.

Ex. 1

A feedstock for thermal spray coating was prepared as follows.

A bulk material of a Fe—Al intermetallic compound having an Al contentof 48 weight % was crushed by a ball mill to obtain a Fe—Alintermetallic compound powder (average particle size: 8 μm). Theproportion of a FeAl₂ intermetallic compound in this powder was about 80weight %.

A powder (average particle size: 5 μm) of a Fe alloy (stainless steel)was prepared by an atomization method, whereupon the proportion of Fe inthis powder was 74 weight %.

The above Fe—Al intermetallic compound powder and the above Fe alloypowder were weighed and mixed in a weight ratio of the Fe—Alintermetallic compound having an Al content of 48 weight % to the Fealloy (stainless steel) being 72:28 so that the weight ratio (Al/Fe) ofAl to Fe in the mixture would be 0.61, and charged into a rotary ballmill, and the resultant was mixed and crushed for 48 hours using ethylalcohol as an organic solvent.

0.5 weight % of polyethylene glycol was added to a slurry obtained, theviscosity was adjusted, and then granulation process was carried outusing a disk atomizer type spray dryer to prepare a granulated powderhaving an average particle size of about 48 μm. This granulated powderwas calcined in an Ar atmosphere at 850° C. for one hour, and thencrushed and classified to obtain a feedstock for thermal spray coatinghaving an average particle size of 42 μm.

On a metal substrate (SUS304 plate) subjected to blast treatment usingan alumina grid, a thermal spray coating film (film thickness: 250 μm)was formed from the feedstock for thermal spray coating obtained by theabove procedure, by means of an atmospheric plasma spraying method.

A cross sectional image after the thermal spray coating film was formed,was photographed by a scanning electron microscope (SEM) (see FIG. 2).In FIG. 2(a), the upper portion corresponds to a resin applied on thesurface of the thermal spray coating film, for cutting the sample, thecenter portion corresponds to the thermal spray coating film, and thelower portion corresponds to the metal substrate. It is observed fromFIG. 2(a) that the formed thermal spray coating film had few pores, andthe adhesion at the interface was favorable. A powder scratched from thecoating film by means of a machining was analyzed by an X-raydiffraction method (XRD), whereby it was confirmed that the constituentphase of the thermal spray coating film formed was a multi-phasestructure containing FeAl and FeAl₂.

FIG. 2(b) is a magnified image in the vicinity of a surface side of athermal spray coating film in FIG. 2(a). The upper portion in FIG. 2(b)corresponds to the above-mentioned resin. FIG. 2(c) is a mapping imageof Al analyzed by EDS of the imaging part of FIG. 2(b). FIG. 2(d) is amapping image of 0 analyzed by EDS of the imaging part of FIG. 2(b). Asis clear from FIG. 2(a) to FIG. 2(d), a mixed powder of the Al—Fe basedintermetallic compound powder and the Fe based metallic powder wasflattened and laminated by heat and collision energy in the thermalspray process to form a multi-phase structure. It is found that, in thevicinity of the surface of the thermal spray coating film, Al₂O₃ isentirely and homogeneously dispersed. Al₂O₃ dispersed in the coatingfilm is less than 5 μm, and therefore a distance between Al₂O₃ beingpresent within 50 μm from the surface layer is at least 5 μm.

FIG. 3(a) is an SEM image showing a cross section of a coating filmformed by calorizing treatment. From the left side of the micrograph, aresin applied for cutting, a void layer and a coating film formed bycalorizing treatment are observed in this order. Here, the void layer isone formed by delamination between the resin and the coating film duringthe cutting. This coating film was formed by the following steps. Astainless steel (SUS304) substrate was mounted in a steel-made casetogether with a Fe—Al alloy powder and a NH₄Cl powder, and the case wassealed, followed by heating at 950° C. in a furnace. The coating filmwas broken only by polishing the surface of the coating film by cuttingthe sample for photographing a SEM image showing a cross section.

FIG. 3(b) is a magnified image in the vicinity of a surface side of thecoating film formed by calorizing treatment in FIG. 3(a). A black regionat a center is one in which Al₂O₃ agglomerated. Other regions are madeof the uniform alloy formed by calorizing. FIG. 3(c) is a mapping imageof Al analyzed by EDS of the imaging part of FIG. 3(b). FIG. 3(d) is amapping image of 0 analyzed by EDS of the imaging part of FIG. 3(b). Asshown in FIGS. 3(b) to (d), on a part of the surface of the coatingfilm, Al₂O₃ is at least agglomerated in a region of 5 μm or more, and ina larger region, it exceeds 10 μm. The coating film formed by calorizingin FIG. 3(a) seems to be almost uniform as a whole, but as shown inFIGS. 3(b) to (d), it is found that a region on which Al₂O₃ isagglomerated is actually present.

FIG. 4 is a result of an energy dispersive X-ray spectrometry (EDS)analysis of a cross section showing a coating film formed by calorizingtreatment (upper graph) and an SEM image at a measurement part thereof(lower figure). Analyzed sections are arrow portions, and a massconcentration obtained by analysis from the surface side to the insideof the substrate by using EDS corresponds to the position of the SEMimage. In the case of the coating film formed by the calorizingtreatment, a diffusion layer is present between the metal substrate andthe Al—Fe based intermetallic compound, the coating film itself appearsto be almost uniform as a whole, the weight ratio of Fe to Al in theintermetallic compound phase is close to 1, and therefore it is possibleto estimate that most of the constituent phase is brittle FeAl₂.

On the other hand, in the case of a coating film having a multi-phasestructure of a Al—Fe based intermetallic compound, even when most of aconstituent phase of the Fe—Al based intermetallic compound is FeAl₂,FeAl having a ductility, produced by a reaction with a metal feedstockduring thermal spray coating, is present close to FeAl₂, and as aresult, a coating film thus produced has a strong toughness as comparedwith a calorized coating film.

Of the above-formed thermal spray coating film, a Vickers hardness(kg/mm²) and a thermal expansion coefficient (α×10⁻⁶/° C.) at atemperature range of from room temperature to 700° C. were measured asfollows.

The Vickers hardness was determined in such a manner that the thermalspray coating sample prepared was cut and polished, and with respect tothe cross section of the polished thermal spray coating film, thehardness was measured on 5 points under a load of 300 g by using a microVickers hardness tester, and the average value was taken as the measuredvalue.

The thermal expansion coefficient (α×10⁻⁶/° C.) was obtained byincreasing the temperature at a rate of 500° C./hr in the air by using avertical push rod dilatometer, followed by measurement within a range offrom room temperature to 700° C.

Comp. Ex. 1

A spherical powder was prepared by atomization method so that a weightratio (Al/Fe) of Al to Fe in the mixture would be 0.33, and thespherical powder was classified to obtain a powder having a size of from20 to 75 μm, which was used as a thermal spray feedstock. This feedstockwas used to prepare a coating sample in the same manner as in Ex. 1, andthe Vickers hardness and the thermal expansion coefficient at atemperature range of from room temperature to 700° C. were measured.Most of the constituent phase of the coating film was FeAl, and wasidentical with a coating film which has been studied heretofore. FIG. 5is a metallographic microscope image of indentations by a Vickershardness tester diamond indenter pressed into the cross section of eachof the coating film of Ex. 1 and the coating film of Comp. Ex. 1, andshows that the hardness of the conventional coating film is much lowerthan that of the coating film of the present invention.

Comp. Ex. 2

A bulk material of an Fe—Al intermetallic compound having an Al contentof 50 weight % was crushed by a ball mill to obtain an Fe—Alintermetallic compound powder (average particle size: 8 μm). Aproportion of the FeAl₂ intermetallic compound in this powder was about70 weight %.

A powder (average particle size: 5 μm) of a Fe alloy (stainless steel)was prepared by an atomization method, and a proportion of Fe in thispowder was 74 weight %.

A thermal spray coating film was formed in the same manner as in Ex. 1except that the above Fe—Al intermetallic compound powder and the Fealloy powder were weighed and charged into a rotary ball mill so thatthe weight ratio (Al/Fe) of Al to Fe in the mixture would be 0.96,followed by mixing and grinding for 48 hours, and the Vickers hardnessand the thermal expansion coefficient at a temperature range of fromroom temperature to 700° C. were measured.

The measurement results of the Vickers hardness and the thermalexpansion coefficient at a temperature range of from room temperature to700° C. were shown in the following Table.

TABLE 1 Al/Fe Thermal weight Vickers expansion Main ratio in hardnesscoefficient constituent mixture kg/mm² ×10⁻⁶ phase Ex. 1 0.61 450 18.5FeAl, FeAl₂ Comp. Ex. 1 0.33 320 22 FeAl Comp. Ex. 2 0.96 780 15FeAl₂—Fe₂Al₅

The thermal spray coating film in Ex. 1 is a coating film having amulti-phase structure containing FeAl and FeAl₂. In the thermal spraycoating film in Ex. 1, the thermal expansion coefficient at atemperature range of from room temperature to 700° C., is substantiallythe same as the thermal expansion coefficient (a thermal expansioncoefficient at from 0 to 649° C. is 18.7×10⁻⁶) of stainless steel(SUS)304 widely used as a metal substrate for a glass-conveying roll,and therefore peeling of the coating film when used as a glass-conveyingroll is reduced.

Further, the Vickers hardness of soda lime silicate glass, which isabout 530 kg/mm² at room temperature, is estimated to be lower than theVickers hardness of a thermal spray coating film of Ex. 1 at atemperature range of from 400 to 800° C. Therefore, the coating filmwill not be damaged by e.g. a cullet when used as a glass-conveyingroll.

A constituent phase of the thermal spray coating film in Comp. Ex. 1 isFeAl. The thermal spray coating film in Comp. Ex. 1 has a low Vickershardness, and is significantly different from SUS304 in thermalexpansion coefficient at a temperature range of from room temperature to700° C., and therefore such a coating film may peel when used as aglass-conveying roll.

A constituent phase of the thermal spray coating film in Comp. Ex. 2 isFeAl₂. The thermal spray coating film in Comp. Ex. 2 has a high Vickershardness but is brittle. Further, the thermal expansion coefficientwithin a temperature range of from room temperature to 700° C. issignificantly different from that of SUS304, and therefore such acoating film may peel when used as a glass-conveying roll.

Ex. 2, Comp. Ex. 3

As a metal substrate, a SUS310S plate was used to form a thermal spraycoating film in the same manner as in Ex. 1. The thermal spray coatingfilm formed was polished with an abrasive of #2000, and then a smallsample of Sn was put on the surface having the thermal spray coatingfilm formed, as shown in FIG. 6 (Ex. 2). A SUS310S plate without thermalspray coating film formed was also polished with an abrasive of #2000,and then a small sample of Sn was put thereon (Comp. Ex. 3). In FIG. 6,the left side shows Comp. Ex. 3, and the right side shows Ex. 2.

These samples were put in a box type electric furnace heated by a MoSi₂heater, and heated at 1,100° C. for one hour in a nitrogen atmosphere.

FIG. 7 shows images after the heating. As shown in FIG. 7, Sn was fixedin Comp. Ex. 3 in which the small sample of Sn was put on the SUS310Splate, but on the other hand, Sn was not fixed in Ex. 2 in which thesmall sample of Sn was put on the surface having the thermal spraycoating film formed, and therefore it was confirmed that the wettabilityof Sn was low. From this result, it is possible to confirm that metaltin or tin oxide is less likely to be adhered on the surface of aglass-conveying roll.

Further, the sample shown in FIG. 6 was surrounded with a carbon piecein a box type electric furnace heated by a MoSi₂ heater, and in thisstate, the sample was heated for one hour at 1,100° C. in a nitrogenatmosphere. In such a state, an oxygen partial pressure around thesample can be suppressed to be lower, whereby wetting and spreading overof Sn is less likely to be inhibited.

FIG. 8 shows images after the heating. As shown in FIG. 8, Sn became wetto spread over the SUS310S plate in Comp. Ex. 3 in which the smallsample of Sn was put on the SUS310S plate, whereby strong bubbling dueto reaction of the SUS310S plate with Sn was confirmed. Sn was not fixedin Ex. 2 in which the small sample of Sn was put on the surface havingthe thermal spray coating film formed, and therefore it was confirmedthat the wettability of Sn was low.

Ex. 3, Comp. Ex. 4

As a metal substrate, a SUS310S plate was used to form a thermal spraycoating film in the same manner as in Ex. 1. The thermal spray coatingfilm formed was polished with an abrasive of #2000, and then a smallsample of alkali glass (AS manufactured by Asahi Glass Company, Limited)was put on the surface having the thermal spray coating film formed, asshown in FIG. 9 (Ex. 3). A SUS310S plate having no thermal spray coatingfilm formed was also polished with an abrasive of #2000, and then asmall sample of alkali glass was put thereon (Comp. Ex. 4). In FIG. 9,the left side shows Ex. 3, and the right side shows Comp. Ex. 4.

These samples were put in a box type electric furnace heated by a MoSi₂heater, and heated for 0.5 hour at 1,100° C. in air.

FIG. 10 shows images after the heating. As shown in FIG. 10, the glassbecame wet to spread over the SUS310S plate in Comp. Ex. 4 in which thesmall sample of alkali glass was put on the SUS310S plate, but on theother hand, glass was adhered to only a part of the thermal spraycoating film, and the glass was also less spread over, in Ex. 3 in whichthe small sample of alkali glass was put on the surface having thethermal spray coating film formed. From these results, it was confirmedthat the wettability of glass was low. From these results, it ispossible to confirm that agglutination of a glass residue to the surfaceof a conveying roll is less likely to occur when such a thermal spraycoating film is used as a glass-conveying roll.

This application is a continuation of PCT Application No.PCT/JP2017/044078, filed on Dec. 7, 2017, which is based upon and claimsthe benefit of priority from Japanese Patent Application No. 2016-248029filed on Dec. 21, 2016. The contents of those applications areincorporated herein by reference in their entireties.

What is claimed is:
 1. A method for forming a thermal spray coatingfilm, comprising: forming a thermal spray coating film of an Al—Fe basedintermetallic compound, on the surface of a metal substrate, from amixture of an Al—Fe based intermetallic compound powder composed mainlyof FeAl₂ and a metal powder composed mainly of Fe, as feedstock.
 2. Themethod according to claim 1, wherein a blend ratio of the intermetalliccompound powder to the metal powder is from 70/30 to 80/20 by the weightratio.
 3. The method according to claim 1, wherein a weight ratio(Al/Fe) of Al to Fe in the mixture is from 0.55 to 0.85.
 4. The methodaccording to claim 1, wherein a weight ratio (Al/Fe) of Al to Fe in theintermetallic compound powder is from 0.90 to 1.15.
 5. The methodaccording to claim 1, wherein a proportion of FeAl₂ in the intermetalliccompound powder is at least 75 weight %.
 6. The method according toclaim 1, wherein a proportion of Fe in the metal powder is at least 70weight %.
 7. The method according to claim 1, wherein a constituentmaterial of the surface of the metal substrate is iron or an iron-basedalloy.
 8. The method according to claim 1, wherein the thermal spraycoating film has a film-thickness of from 0.05 to 1.5 mm.
 9. A methodfor producing a metal product, comprising: forming a thermal spraycoating film of an Al—Fe based intermetallic compound on the surface ofa metal substrate by the method as defined in claim 1, to produce ametal product comprising the metal substrate having the thermal spraycoating film.
 10. The method according to claim 9, wherein the metalproduct is a glass-conveying roll.
 11. A thermal spray coating film ofan Al—Fe based intermetallic compound, which has a multi-phase structurein a scanning electron microscopic (SEM) image showing a cross-sectionof the thermal spray coating film of an Al—Fe based intermetalliccompound.
 12. The thermal spray coating film according to claim 11,wherein a weight ratio (Al/Fe) of Al to Fe in the thermal spray coatingfilm is from 0.55 to 0.85.
 13. The thermal spray coating film accordingto claim 11, which contains Al₂O₃ particles having a size of less than 5μm.
 14. The thermal spray coating film according to claim 11, wherein adistance between Al₂O₃ particles being present within 50 μm from asurface layer of the thermal spray coating film, is at least 5 μm.
 15. Aglass-conveying roll comprising a metal roll having the thermal spraycoating film as defined in claim 11 on its surface.